Download Review Article Bcl-2:Beclin 1 complex: multiple, mechanisms

Am J Cancer Res 2012;2(2):214-221
www.ajcr.us /ISSN:2156-6976/ajcr0000098
Review Article
Bcl-2:Beclin 1 complex: multiple, mechanisms regulating
autophagy/apoptosis toggle switch
Rebecca T. Marquez, Liang Xu
University of Kansas, Department of Molecular Biosciences, Lawrence, Kansas, USA
Received December 21, 2011; accepted January 6, 2012; Epub February 15, 2012; Published February 28, 2012
Abstract: Cancer cells have developed novel mechanisms for evading chemotherapy-induced apoptosis and autophagy-associated cell death pathways. Upon the discovery that chemotherapeutics could target these cell death pathways in a manner that was not mutually exclusive, new discoveries about the interrelationship between these two
pathways are emerging. Key proteins originally thought to be “autophagy-related proteins” are now found to be involved in either inducing or inhibiting apoptosis. Similarly, apoptosis inhibiting proteins can also block autophagyassociated cell death. One example is the complex formed by the autophagy protein, Beclin 1, and anti-apoptotic
protein Bcl-2, which leads to inhibition of autophagy-associated cell death. Researchers have been investigating additional mechanisms that form/disrupt this complex in order to better design chemotherapeutics. This review will highlight the role Bcl-2 and Beclin 1 play in cancer development and drug resistance, as well as the role the Bcl-2:Beclin 1
complex in the switch between autophagy and apoptosis.
Keywords: Apoptosis, autophagy, Bcl-2, Beclin 1, Gossypol, BH3 mimetics
Introduction
Autophagy is a catabolic pathway activated by
cellular stress, such as starvation or pathogen
infection, followed by engulfment of proteins
and organelles by double-membrane vesicles,
called autophagosomes. Autophagy can result
in cellular adaptation, as well as cell survival or
cell death. The ability of autophagy to play a role
in both survival and cell death is counterintuitive. In addition, autophagy demonstrates tumor
suppressive qualities, whereby deficiency in
autophagy leads to cellular transformation and
tumor development [1-3]. Alternatively, cancer
cells can also exploit the benefits of autophagy
by inducing cell survival associated with the
stressful tumor microenvironment [4], as well as
damage caused by chemo- and radiotherapies
[5-7]. Therefore, while autophagy demonstrates
tumor suppressive actions, it also can confer
oncogenicity associated with drug and radioresistance.
Resistance of cancer cells to treatment can be
associated with both autophagy and inhibition
of the more common apoptosis cell death path-
way. Apoptosis resistance in developing novel
cancer therapies has been a tremendous challenge with current chemotherapies. However, a
greater understanding of the interrelationship
between apoptosis and autophagy is providing
precedence for developing new drugs, such as
BH3 mimetics, that can induce autophagyassociated cell death in apoptotic resistance
cells. It is well established that suppression of
apoptosis induces autophagy, while autophagy
inhibition causes apoptosis [8, 9]. Identifying
the “toggle switch” or regulatory mechanisms
involved in the interrelationship between apoptosis- and autophagy-associated cell death is
imperative for creating optimal chemotherapeutics and inhibiting cancer cell growth. Exploiting
these regulatory mechanisms may provide new
targets for developing cancer therapeutics.
Throughout this review, we will discuss chemotherapies and mechanisms for inducing cell
death via the autophagy cell death pathway.
However, it is important to note that while autophagy cell death was previously considered one
of the main cell death pathways [10], independent autophagy cell death may only exist in a few
Autophagy-apoptosis toggle switch by Bcl-2:Beclin 1
exceptional cases, such as Drosophila development [11]. Accumulating evidence is challenging the concept of autophagic cell death in
mammalian cells [12-14]. This debate provides
precedence for developing additional experiments to truly dissect whether cell death associated with autophagy is actually autophagy cell
death or cell death via a combination of death
pathways, such as apoptosis, autophagy, and
necrosis. Furthermore, this examination has led
to re-evaluating modes of cell death and creating additional molecular definitions of cell death
subroutines for greater classification and clarity
[15].
Bcl-2:Beclin 1 interaction regulates autophagy
tigating the role of autophagy during tumorigenesis, identified Beclin 1 as a tumor suppressor. Initial studies showed Beclin 1 expression
was lower in cancer cells versus normal epithelial cells [7]. Heterozygous disruption of BECN1
promotes tumorigenesis [1], while overexpression inhibits tumorigenesis [23]. Clinical studies
have demonstrated that BECN1 is lost in 40% to
75% of breast and ovarian cancers [23]. In addition, downregulation of BECN1 has been shown
in many types of cancers and associated with
poor prognosis [24-29]. Therefore, the reduced
expression of Beclin 1 reduces autophagic removal of damaged organelles that generate
reactive oxygen species and genotoxic stress,
resulting in cellular transformation.
Beclin 1 and Bcl-2 expression levels regulate
autophagic-apoptotic switch
Bcl-2 expression is upregulated in many human
cancers and mediates the resistance of cancers
to chemotherapeutic agents and radiotherapy
[30, 31]. Bcl-2 is overexpressed in 60% of
breast cancer patients. Furthermore, breast
cancer patients with a positive Bcl-2 expression
have shown a poor response to chemotherapy
compared with those that had less Bcl-2 expression [32]. Inhibiting Bcl-2 expression has been
shown to increase the efficacy of drug treatment by inducing apoptosis and autophagy. In
MCF-7 cells, downregulation of Bcl-2 by RNA
interference induced cell death 50% above control, however, apoptosis only accounted for 11%
of this cell death at 96 hours [33]. It is possible
that autophagic cell death was responsible for
the additional cell death not measured by
TUNEL assay. Furthermore, cell death was enhanced by etoposide and doxorubicin treatment
in MCF-7 human breast cancer cells [33]. It was
not determined whether this increase was due
to apoptotic or autophagic cell death. A more
recent study demonstrated that inhibiting Bcl-2
in breast cancer cells via siRNA knockdown did
not induce apoptosis as expected, however induced autophagic cell death [34]. This autophagic cell death was increased by combination
treatment with doxorubicin, which increased
expression of Beclin 1 [34]. Therefore, patient
screening for Bcl-2 expression and Beclin 1 is
important in determining what type of chemotherapy or combination treatment should be
utilized for treating patients.
The expression levels of Beclin 1 and Bcl-2 are
key determinants as to whether cells are resistant to apoptosis or autophagy during tumorigenesis and chemotherapy. Early studies inves-
Initial discoveries investigating the interaction
between Bcl-2 and Beclin 1 were carried out
using overexpression/inhibition studies. HT-29
colon carcinoma cells, which do not express
The Bcl-2 family of proteins, Bcl-2, Bcl-xL and
Mcl-1, are well-known anti-apoptotic mediators;
however, their roles in inhibiting autophagy are
becoming more understood. The cytoprotective
function of Bcl-2 proteins stems from their ability to antagonize Bax and Bak, and thus prevent
apoptosis. Beclin 1, a Bcl-2 homology 3 (BH3)
domain only protein [16], is an essential initiator of autophagy. Beclin 1 recruits key autophagic proteins to a pre-autophagosomal structure,
thereby forming the core complex consisting of
Beclin 1, Vps34, and Vps15 [17]. In addition,
Beclin 1 is a key determining factor as to
whether cells undergo autophagy or apoptosis
[18]. Beclin 1 has been shown to interact via its
BH3 domain with anti-apoptotic Bcl-2 family
members [19]. This interaction prevents Beclin
1 from assembling the pre-autophagosomal
structure, thereby inhibiting autophagy [19]. The
dual role of Bcl-2 and Bcl-xL in inhibiting both
apoptosis and autophagic-associated cell death
makes these proteins ideal chemotherapeutic
targets. BH3 mimetics, such as (-)-gossypol,
obatoclax and ABT-737, disrupt the Bcl2:Beclin1 interaction and currently are undergoing clinical trials [20, 21]. In addition to being
promising new therapies, BH3 mimetics are
providing additional insight into the autophagyapoptosis regulatory pathways, as discussed
below [22].
215
Am J Cancer Res 2012;2(2):214-221
Autophagy-apoptosis toggle switch by Bcl-2:Beclin 1
phagy) is a key regulator of autophagy and has
been shown to interact with both Beclin 1 and
Bcl-2. In response to autophagic stimuli, unc-51
-like kinase 1 (Ulk1) phosphorylates AMBRA1,
which results in AMBRA1 dissociation from the
Dynein motor complex [37]. After dissociation,
AMBRA1 translocates to the ER, binds to Beclin
1 in the autophagy initiation complex [37],
which results in the induction of autophagy.
Alternatively, a recent study demonstrated that
Bcl-2 localized to the mitochondria can also
bind AMBRA1, but ER-localized Bcl-2 does not
[38]. The Bcl-2:AMBRA1 interaction at the mitochondria is downregulated during autophagy, as
well as during apoptosis. Therefore, Bcl-2 can
regulate Beclin 1-induced autophagy by direct
binding to Beclin 1, as well as by sequestering
the activator of Beclin 1 [38].
Figure 1. Bcl-2 can inhibit both autophagy- and apoptosis-associated cell death. Bcl-2 binds to Bak/Bax,
therefore preventing apoptosis. Bcl-2 binds to Beclin
1, preventing assembly of the pre-autophagosomal
structure, which results in inhibition of autophagy.
detectable levels of Bcl-2, were stably transfected with Bcl-2 expression vector. It was found
that only HT-29 cells stably expressing Bcl-2
could inhibit starvation-induced autophagy via
disrupting the Beclin 1/Vps34 complex. Transfecting HeLa cells, an autophagy-competent cell
line that expresses Bcl-2, with Bcl-2 siRNA increased the level of starvation-induced autophagy [35]. This demonstrated that Bcl-2 exerts
an inhibitory effect on autophagy (Figure 1).
Cellular localization and binding partners
In addition to Beclin 1 and Bcl-2 expression levels, cellular localization is a determining factor
regarding the effects of Bcl-2:Beclin 1 interaction on autophagy and apoptosis. Initial studies
demonstrated that Bcl-2 and Beclin 1 interact at
the endoplasmic reticulum (ER) and mitochondria [35]. However, it appears that only Bcl2:Beclin 1 localization to the ER results in inhibition of autophagy. Interestingly, a recent study
[36] demonstrated that NAF-1 (nutrientdeprivation autophagy factor-1) binds Bcl-2 at
the ER, independent of a BH3 domain, and is
required for Bcl-2 to inhibit Beclin 1-mediated
autophagy. Beclin 1 and Bcl-2 can form complexes with additional autophagy regulatory proteins at different cellular locations. AMBRA1
(activating molecule in Beclin 1-regulated auto-
216
Proteins capable of disrupting the Bcl-2:Beclin 1
complex and inducing autophagy are becoming
more evident. High mobility group box 1
(HMGB1), a chromatin-associated nuclear protein and extracellular damage-associated molecular pattern molecule (DAMP), is a novel Beclin 1-binding protein important in sustaining
autophagy. HMGB1 competes with Bcl-2 for
interaction with Beclin 1, and orients Beclin 1 to
autophagosomes [39]. BNIP3 is another protein
that inhibits the Bcl-2:Beclin 1 complex, conversely via binding to Bcl-2. It was reported that
via its BH3 domain, BNIP3 is capable of binding
to Bcl-2, thereby disrupting the interaction between Bcl-2 and Beclin 1, and inducing autophagy [40]. Therefore, competitive proteins,
such as HMGB1 and BNIP3, demonstrate another mechanism for inducing autophagy by
competing with Bcl-2 or Beclin 1.
Phoshorylation regulation
As discussed previously, the cellular localization
and complex formation of Beclin 1 and its regulatory proteins is important for determining
whether cells undergo apoptosis or autophagy.
This cellular location and complex formation is
regulated by phosphorylation of key kinases.
The dissociation of Bcl-2:Beclin 1 complex can
occur by phosphorylation of Bcl-2 by stressactivated c-Jun N-terminal protein kinase 1
(JNK1) [41]. Furthermore, only the ER-enriched
pool of Bcl-2 is subjected to regulation of Beclin
1 binding by JNK1-mediated phosphorylation
[41], another indication that regulatory mechanisms occur at particular subcellular locations.
Am J Cancer Res 2012;2(2):214-221
Autophagy-apoptosis toggle switch by Bcl-2:Beclin 1
Once Bcl-2 is phosphorylated and dissociates
from Beclin 1, autophagy can occur [41]. Upon
continued JNK pathway activation and Bcl-2
phosphorylation, the cells will eventually undergo apoptosis via caspase 3 activation [41].
Death-associated protein kinase (DAPK) is also
involved in regulating the Bcl-2:Beclin 1 complex. DAPK phosphorylates a threonine within
the BH3 domain of Beclin 1, which induces dissociation and allows autophagy to proceed [42].
Apoptosis-induced cleavage of autophagy proteins
Cleavage of key autophagy-related proteins,
such as Beclin 1 and ATG5, is another regulatory mechanism involved in disrupting the Bcl2:Beclin 1 complex. Beclin 1 is a key inducer of
autophagy, but can also be cleaved by caspase
8 during chemotherapy-induced apoptosis [43].
Once Beclin 1 is cleaved, it remains cytosolic
and cannot induce either autophagy or apoptosis, therefore, rendering the protein nonfunctioning. Cells expressing a Beclin 1 mutant
are incapable of being cleaved and less sensitive to chemotherapy in vivo [43]. Therefore,
chemotherapy-associated cleavage of Beclin 1
would ultimately disrupt the Bcl-2:Beclin1 complex, and allow cells to undergo apoptosis upon
treatment. Another study demonstrated, that
following cleavage of Beclin 1, the C-terminus of
cleaved Beclin (Beclin 1-C) can acquire a new
apoptosis-promoting function by translocating
from the cytosol to the mitochondria, inducing
apoptosis in response to interleukin-3 deprivation [44]. Furthermore, using a cell free system,
isolated mitochondria were able to release proapoptotic factors when combined with recombinant Beclin 1-C protein [44]. Therefore, Beclin 1
can be involved in both autophagy and apoptosis depending upon the presence of the fulllength or cleaved form.
ATG5 plays an essential role in inducing autophagy by forming the pre-autophagosome structure. In addition to regulating autophagy, ATG5
also functions as a pro-apoptotic protein. Upon
apoptotic stimuli, calpain, a calcium-dependent
protease, cleaves ATG5 producing a fragment
(tATG5) which contains the amino-terminal portion of ATG5 [45]. tATG5 then translocates to
the mitochondria, triggers cytochrome c release
and caspase activation [45]. Overexpression of
Bcl-2 abrogated the effect of tATG5 on cell
death. Furthermore, tATG5 can disrupt the anti-
217
apoptotic Bcl-xL-Bax complex by binding to BclxL which allows the Bax-Bax complex to form,
inducing apoptosis [45].
BH3 mimetics: exploiting the interaction between Bcl-2 and Beclin1 and identifying new
regulatory pathways
This review has discussed many mechanisms
that regulate the Bcl-2:Beclin 1 complex, including Beclin 1 and Bcl-2 expression levels, cellular
localization, and phosphorylation. BH3 mimetics
are chemotherapies that bind to Bcl-2 and disrupt the Bcl-2:Beclin 1 complex and induce
autophagy-associated cell death. In addition to
demonstrating promise as therapy in clinical
trials, BH3 mimetics have provided beneficial
insight into the regulation of the Bcl-2:Beclin 1
interaction as well as identifying additional pathways that are involved in autophagic cell death.
Recent studies from our lab compared treatment with the natural BH3-mimetic, (-)-gossypol
in treating apoptosis-resistant prostate cancer
cells with high levels of Bcl-2 versus prostate
cancer cells with low Bcl-2 expression [46]. (-)Gossypol induces similar levels of total cell
death in both prostate cancer cell lines, however, the mode of cell death depends upon the
expression of the Bcl-2 family of proteins [20].
In prostate cancer cells with low Bcl-2 expression, more than 80 percent of cells died via
apoptotic cell death. Conversely, in prostate
cancer cells with high Bcl-2 expression, more
than 60 percent died via induction of the autophagy pathway. This death can be blocked by
the apoptosis inhibitor Z-VAD in low Bcl-2 expressing cells and the autophagy inhibitor 3-MA
or Atg5/Beclin 1 siRNAs in high Bcl-2 expressing
cells. Thus, the level of Bcl-2 determines which
type of cell death will be dominant in prostate
cancer cells after treatment with the Bcl-2 inhibitor (-)-gossypol. Furthermore, overexpressing
Bcl-2 decreased the level of (-)-gossypol-induced
autophagy, possibly due to the stoichiometric
abundance of Bcl-2 sequestering Beclin 1 and
inhibiting autophagy induction [46]. Similar results were also observed with other BH3mimetics, ABT-236 and ABT-737 ([47] and Lian
and Marquez, manuscript in preparation), indicating that this phenomenon is not compound
specific. These data suggests that Bcl-2 expression levels may be a key marker in determining
whether to utilize BH3 mimetics for chemotherapy when treating patients.
Am J Cancer Res 2012;2(2):214-221
Autophagy-apoptosis toggle switch by Bcl-2:Beclin 1
Figure 2. BH3 mimetics (i.e. (-)-Gossypol, ABT-236, ABT-737, HA14-1) bind Bcl-2 and prevent Bcl-2 inhibition of autophagy- and apoptosis-associated cell death. BH3 mimetics can also induce autophagy by activating JNK, Sirtuin 1,
AMPK, IKK Kinase as well as inhibiting mTOR and depleting cytoplasmic p53.
Our research also demonstrated that the BH3mimetic (-)-gossypol induces autophagy via
blocking Bcl-2:Beclin 1 interaction at the ER
[46]. Upon overexpression of Bcl-2, the complex
of Bcl-2:Beclin 1 on ER membranes is interrupted by (-)-gossypol prior to the complex of Bcl
-2:Bak/Bax on mitochondria [46]. After treatment with (-)-gossypol, Beclin 1 is liberated from
Bcl-2 in conjunction with transcriptional upregulation [46]. Together, these events trigger the
autophagic cascade. Therefore, autophagic cell
death via (-)-gossypol is Beclin 1-dependent
[20]. Our data are consistent with that of the
BH3 mimetic, ABT-737, which also induces
autophagy by disrupting the Bcl-2:Beclin 1 complex formed at the ER and not mitochondria
[47]. In addition, our lab has also found that (-)gossypol can induce JNK signaling and subsequent phosphorylation of Bcl-2, disrupting the
Bcl-2:Beclin 1 complex (Lian and Marquez,
manuscript in preparation).
As previously discussed, BH3 mimetics induce
autophagy by disrupting the Bcl-2:Beclin 1 inhibitory complex. A recent compelling study has
demonstrated that BH3 mimetics, ABT-737 and
218
HA14-1, also stimulate other pro-autophagic
pathways and hence activate the nutrient sensors Sirtuin 1 and AMPK, inhibit mTOR, deplete
cytoplasmic p53, and trigger the IKK Kinase
[22]. Activation of autophagy was independent
of reduced oxidative phosphorylation or reduced
cellular ATP concentrations. Furthermore, induction of autophagy by ATBT-737 and HA14-1 was
completely inhibited by knockdown of Beclin 1
or Vps34. This suggests that BH3 mimetics can
act across multiple pathways, eliciting a coordinated effort to maximally induce autophagy. In
addition, disrupting the Bcl-2:Beclin 1 complex,
elicits a signaling response that induces multiple signals activating autophagy (Figure 2).
Conclusions and future directions
As this review outlines, multiple mechanisms
regulate the autophagy- inhibiting Bcl-2:Beclin 1
complex. The expression levels of Bcl-2 and
Beclin 1 have demonstrated the importance of
the affinity for each component in maintaining
or disrupting this inhibitory complex. The discovery of binding partners that alter the affinity of
Bcl-2:Beclin 1 for one another, are also becom-
Am J Cancer Res 2012;2(2):214-221
Autophagy-apoptosis toggle switch by Bcl-2:Beclin 1
ing more evident. Cellular location, whereby the
complex is formed at the ER or mitochondria,
are also important contributing factors as to
whether this complex affects autophagy. More
drug treatment research studies are demonstrating that overriding and disrupting the Bcl2:Beclin 1 complex occurs by phosphorylation of
key kinases, especially JNK phosphorylation of
Bcl-2. Developing combination therapies between BH3 mimetics and JNK activators will
provide a greater “double-hit” effect in disrupting the Bcl-2:Beclin 1 complex, eventually leading cancer cells to autophagic/apoptotic cell
death. Identifying the major mechanisms that
maintain/disrupt this complex will allow us to
develop additional drug treatments that can
target this complex from many approaches ensuring a greater therapeutic outcome.
[8]
[9]
[10]
[11]
Address correspondence to: Dr. Rebecca T. Marquez
and Dr. Liang Xu, University of Kansas, Department of
Molecular Biosciences, Lawrence, Kansas, USA Email: [email protected]; [email protected]
[12]
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
219
Qu X, Yu J, Bhagat G, Furuya N, Hibshoosh H,
Troxel A, Rosen J, Eskelinen EL, Mizushima N,
Ohsumi Y, Cattoretti G and Levine B. Promotion
of tumorigenesis by heterozygous disruption of
the beclin 1 autophagy gene. The Journal of
clinical investigation 2003; 112: 1809-1820.
Edinger AL, Thompson CB. Defective autophagy
leads to cancer. Cancer cell 2003; 4: 422-424.
Yue Z, Jin S, Yang C, Levine AJ and Heintz N.
Beclin 1, an autophagy gene essential for early
embryonic development, is a haploinsufficient
tumor suppressor. Proceedings of the National
Academy of Sciences of the United States of
America 2003; 100: 15077-15082.
Rouschop KM, Wouters BG. Regulation of autophagy through multiple independent hypoxic
signaling pathways. Current molecular medicine 2009; 9: 417-424.
Lomonaco SL, Finniss S, Xiang C, Decarvalho A,
Umansky F, Kalkanis SN, Mikkelsen T and Brodie C. The induction of autophagy by gammaradiation contributes to the radioresistance of
glioma stem cells. International journal of cancer. Journal international du cancer 2009; 125:
717-722.
Kuwahara Y, Oikawa T, Ochiai Y, Roudkenar
MH, Fukumoto M, Shimura T, Ohtake Y, Ohkubo
Y, Mori S and Uchiyama Y. Enhancement of
autophagy is a potential modality for tumors
refractory to radiotherapy. Cell death & disease
2011; 2: e177.
Kondo Y, Kanzawa T, Sawaya R and Kondo S.
The role of autophagy in cancer development
[13]
[14]
[15]
[16]
[17]
[18]
[19]
and response to therapy. Nature reviews. Cancer 2005; 5: 726-734.
Maiuri MC, Zalckvar E, Kimchi A and Kroemer
G. Self-eating and self-killing: crosstalk between autophagy and apoptosis. Nature reviews. Molecular cell biology 2007; 8: 741-752.
Platini F, Perez-Tomas R, Ambrosio S and Tessitore L. Understanding autophagy in cell death
control. Current pharmaceutical design 2010;
16: 101-113.
Kroemer G, Galluzzi L, Vandenabeele P,
Abrams J, Alnemri ES, Baehrecke EH, Blagosklonny MV, El-Deiry WS, Golstein P, Green DR,
Hengartner M, Knight RA, Kumar S, Lipton SA,
Malorni W, Nunez G, Peter ME, Tschopp J, Yuan
J, Piacentini M, Zhivotovsky B and Melino G.
Classification of cell death: recommendations
of the Nomenclature Committee on Cell Death
2009. Cell death and differentiation 2009; 16:
3-11.
Denton D, Shravage B, Simin R, Baehrecke EH
and Kumar S. Larval midgut destruction in Drosophila: not dependent on caspases but suppressed by the loss of autophagy. Autophagy
2010; 6: 163-165.
Shen HM, Codogno P. Autophagic cell death:
Loch Ness monster or endangered species?
Autophagy 2011; 7: 457-465.
Shen S, Kepp O and Kroemer G. The end of
autophagic cell death? Autophagy 2012; 8.
[Epub ahead of print]
Shen S, Kepp O, Michaud M, Martins I, Minoux
H, Metivier D, Maiuri MC, Kroemer RT and Kroemer G. Association and dissociation of autophagy, apoptosis and necrosis by systematic
chemical study. Oncogene 2011; 30: 45444556.
Galluzzi L, Vitale I, Abrams JM, Alnemri ES, Baehrecke EH, Blagosklonny MV, Dawson TM, Dawson VL, El-Deiry WS, Fulda S, Gottlieb E, Green
DR, Hengartner MO, Kepp O, Knight RA, Kumar
S, Lipton SA, Lu X, Madeo F, Malorni W, Mehlen
P, Nunez G, Peter ME, Piacentini M,
Rubinsztein DC, Shi Y, Simon HU, Vandenabeele P, White E, Yuan J, Zhivotovsky B, Melino
G and Kroemer G. Molecular definitions of cell
death subroutines: recommendations of the
Nomenclature Committee on Cell Death 2012.
Cell death and differentiation 2012; 19: 107120.
Oberstein A, Jeffrey PD and Shi Y. Crystal structure of the Bcl-XL-Beclin 1 peptide complex:
Beclin 1 is a novel BH3-only protein. The Journal of biological chemistry 2007; 282: 1312313132.
He C, Levine B. The Beclin 1 interactome. Current opinion in cell biology 2010; 22: 140-149.
Kang R, Zeh HJ, Lotze MT and Tang D. The Beclin 1 network regulates autophagy and apoptosis. Cell death and differentiation 2011; 18:
571-580.
Liang XH, Kleeman LK, Jiang HH, Gordon G,
Am J Cancer Res 2012;2(2):214-221
Autophagy-apoptosis toggle switch by Bcl-2:Beclin 1
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
220
Goldman JE, Berry G, Herman B and Levine B.
Protection against fatal Sindbis virus encephalitis by beclin, a novel Bcl-2-interacting protein.
Journal of virology 1998; 72: 8586-8596.
Lian J, Karnak D and Xu L. The Bcl-2-Beclin 1
interaction in (-)-gossypol-induced autophagy
versus apoptosis in prostate cancer cells. Autophagy 2010; 6: 1201-1203.
Oltersdorf T, Elmore SW, Shoemaker AR, Armstrong RC, Augeri DJ, Belli BA, Bruncko M,
Deckwerth TL, Dinges J, Hajduk PJ, Joseph MK,
Kitada S, Korsmeyer SJ, Kunzer AR, Letai A, Li
C, Mitten MJ, Nettesheim DG, Ng S, Nimmer
PM, O'Connor JM, Oleksijew A, Petros AM, Reed
JC, Shen W, Tahir SK, Thompson CB, Tomaselli
KJ, Wang B, Wendt MD, Zhang H, Fesik SW and
Rosenberg SH. An inhibitor of Bcl-2 family proteins induces regression of solid tumours. Nature 2005; 435: 677-681.
Malik SA, Orhon I, Morselli E, Criollo A, Shen S,
Marino G, BenYounes A, Benit P, Rustin P, Maiuri MC and Kroemer G. BH3 mimetics activate
multiple pro-autophagic pathways. Oncogene
2011; 30: 3918-3929.
Liang XH, Jackson S, Seaman M, Brown K,
Kempkes B, Hibshoosh H and Levine B. Induction of autophagy and inhibition of tumorigenesis by beclin 1. Nature 1999; 402: 672-676.
Miracco C, Cosci E, Oliveri G, Luzi P, Pacenti L,
Monciatti I, Mannucci S, De Nisi MC, Toscano
M, Malagnino V, Falzarano SM, Pirtoli L and
Tosi P. Protein and mRNA expression of autophagy gene Beclin 1 in human brain tumours.
International journal of oncology 2007; 30: 429
-436.
Shi YH, Ding ZB, Zhou J, Qiu SJ and Fan J. Prognostic significance of Beclin 1-dependent apoptotic activity in hepatocellular carcinoma. Autophagy 2009; 5: 380-382.
Ahn CH, Jeong EG, Lee JW, Kim MS, Kim SH,
Kim SS, Yoo NJ and Lee SH. Expression of beclin-1, an autophagy-related protein, in gastric
and colorectal cancers. APMIS: acta
pathologica, microbiologica, et immunologica
Scandinavica 2007; 115: 1344-1349.
Wan XB, Fan XJ, Chen MY, Xiang J, Huang PY,
Guo L, Wu XY, Xu J, Long ZJ, Zhao Y, Zhou WH,
Mai HQ, Liu Q and Hong MH. Elevated Beclin 1
expression is correlated with HIF-1alpha in
predicting poor prognosis of nasopharyngeal
carcinoma. Autophagy 2010; 6: 395-404.
Huang JJ, Li HR, Huang Y, Jiang WQ, Xu RH,
Huang HQ, Lv Y, Xia ZJ, Zhu XF, Lin TY and Li
ZM. Beclin 1 expression: a predictor of prognosis in patients with extranodal natural killer Tcell lymphoma, nasal type. Autophagy 2010; 6:
777-783.
Shen Y, Li DD, Wang LL, Deng R and Zhu XF.
Decreased expression of autophagy-related
proteins in malignant epithelial ovarian cancer.
Autophagy 2008; 4: 1067-1068.
Huang Z. Bcl-2 family proteins as targets for
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
anticancer drug design. Oncogene 2000; 19:
6627-6631.
Karnak D, Xu L. Chemosensitization of prostate
cancer by modulating Bcl-2 family proteins.
Curr Drug Targets 2010; 11: 699-707.
Buchholz TA, Garg AK, Chakravarti N, Aggarwal
BB, Esteva FJ, Kuerer HM, Singletary SE, Hortobagyi GN, Pusztai L, Cristofanilli M and Sahin
AA. The nuclear transcription factor kappaB/bcl
-2 pathway correlates with pathologic complete
response to doxorubicin-based neoadjuvant
chemotherapy in human breast cancer. Clinical
cancer research: an official journal of the
American Association for Cancer Research
2005; 11: 8398-8402.
Lima RT, Martins LM, Guimaraes JE, Sambade
C and Vasconcelos MH. Specific downregulation of bcl-2 and xIAP by RNAi enhances the
effects of chemotherapeutic agents in MCF-7
human breast cancer cells. Cancer gene therapy 2004; 11: 309-316.
Akar U, Chaves-Reyez A, Barria M, Tari A, Sanguino A, Kondo Y, Kondo S, Arun B, LopezBerestein G and Ozpolat B. Silencing of Bcl-2
expression by small interfering RNA induces
autophagic cell death in MCF-7 breast cancer
cells. Autophagy 2008; 4: 669-679.
Pattingre S, Tassa A, Qu X, Garuti R, Liang XH,
Mizushima N, Packer M, Schneider MD and
Levine B. Bcl-2 antiapoptotic proteins inhibit
Beclin 1-dependent autophagy. Cell 2005; 122:
927-939.
Chang NC, Nguyen M, Germain M and Shore
GC. Antagonism of Beclin 1-dependent autophagy by BCL-2 at the endoplasmic reticulum
requires NAF-1. The EMBO journal 2010; 29:
606-618.
Di Bartolomeo S, Corazzari M, Nazio F, Oliverio
S, Lisi G, Antonioli M, Pagliarini V, Matteoni S,
Fuoco C, Giunta L, D'Amelio M, Nardacci R,
Romagnoli A, Piacentini M, Cecconi F and Fimia
GM. The dynamic interaction of AMBRA1 with
the dynein motor complex regulates mammalian autophagy. The Journal of cell biology 2010;
191: 155-168.
Strappazzon F, Vietri-Rudan M, Campello S,
Nazio F, Florenzano F, Fimia GM, Piacentini M,
Levine B and Cecconi F. Mitochondrial BCL-2
inhibits AMBRA1-induced autophagy. The
EMBO journal 2011; 30: 1195-1208.
Tang D, Kang R, Livesey KM, Cheh CW, Farkas
A, Loughran P, Hoppe G, Bianchi ME, Tracey KJ,
Zeh HJ, 3rd and Lotze MT. Endogenous HMGB1
regulates autophagy. The Journal of cell biology
2010; 190: 881-892.
Bellot G, Garcia-Medina R, Gounon P, Chiche J,
Roux D, Pouyssegur J and Mazure NM. Hypoxiainduced autophagy is mediated through hypoxia-inducible factor induction of BNIP3 and
BNIP3L via their BH3 domains. Molecular and
cellular biology 2009; 29: 2570-2581.
Wei Y, Pattingre S, Sinha S, Bassik M and Le-
Am J Cancer Res 2012;2(2):214-221
Autophagy-apoptosis toggle switch by Bcl-2:Beclin 1
vine B. JNK1-mediated phosphorylation of Bcl-2
regulates starvation-induced autophagy. Molecular cell 2008; 30: 678-688.
[42] Zalckvar E, Berissi H, Eisenstein M and Kimchi
A. Phosphorylation of Beclin 1 by DAP-kinase
promotes autophagy by weakening its interactions with Bcl-2 and Bcl-XL. Autophagy 2009; 5:
720-722.
[43] Li H, Wang P, Sun Q, Ding WX, Yin XM, Sobol
RW, Stolz DB, Yu J and Zhang L. Following cytochrome c release, autophagy is inhibited during
chemotherapy-induced apoptosis by caspase 8mediated cleavage of Beclin 1. Cancer research 2011; 71: 3625-3634.
[44] Wirawan E, Vande Walle L, Kersse K, Cornelis
S, Claerhout S, Vanoverberghe I, Roelandt R,
De Rycke R, Verspurten J, Declercq W, Agostinis
P, Vanden Berghe T, Lippens S and Vandenabeele P. Caspase-mediated cleavage of Beclin1 inactivates Beclin-1-induced autophagy and
enhances apoptosis by promoting the release
of proapoptotic factors from mitochondria. Cell
death & disease 2010; 1: e18.
221
[45] Yousefi S, Perozzo R, Schmid I, Ziemiecki A,
Schaffner T, Scapozza L, Brunner T and Simon
HU. Calpain-mediated cleavage of Atg5
switches autophagy to apoptosis. Nature cell
biology 2006; 8: 1124-1132.
[46] Lian J, Wu X, He F, Karnak D, Tang W, Meng Y,
Xiang D, Ji M, Lawrence TS and Xu L. A natural
BH3 mimetic induces autophagy in apoptosisresistant prostate cancer via modulating Bcl-2Beclin1 interaction at endoplasmic reticulum.
Cell death and differentiation 2011; 18: 60-71.
[47] Maiuri MC, Le Toumelin G, Criollo A, Rain JC,
Gautier F, Juin P, Tasdemir E, Pierron G, Troulinaki K, Tavernarakis N, Hickman JA, Geneste O
and Kroemer G. Functional and physical interaction between Bcl-X(L) and a BH3-like domain
in Beclin-1. The EMBO journal 2007; 26: 25272539.
Am J Cancer Res 2012;2(2):214-221